CVE-2026-59198
Summary
Pillow's TGA RLE encoder reads past its row buffer when saving a mode "1"
image. Adjacent process heap bytes can be copied into the generated TGA file.
The bug is reachable through the public save API:
im.save(out, format="TGA", compression="tga_rle")
Older affected Pillow versions use the equivalent public option rle=True.
For mode "1", Pillow allocates a packed row buffer of ceil(width / 8)
bytes, but ImagingTgaRleEncode() treats the row as one full byte per pixel.
The maximum valid TGA width is 65535. At that width:
allocated packed row buffer: 8192 bytes
encoder byte-offset walk: 65535 bytes
maximum OOB window per row: 57343 bytes
On non-ASAN Pillow 12.2.0, the public-only maximum-width PoC below serialized
57297 bytes from distinct out-of-bounds source offsets into one returned TGA,
covering 99.92% of the maximum adjacent heap window. No heap grooming, ctypes,
private API, or malformed input file was used. The disclosure is emitted across
many TGA packet payload copies of at most 128 bytes each, not one large
memcpy().
Details
src/PIL/TgaImagePlugin.py allows mode "1" TGA output and selects the
tga_rle encoder when RLE compression is requested.
src/encode.c:_setimage() allocates the row buffer using the packed-bit
formula:
state->bytes = (state->bits * state->xsize + 7) / 8;
state->buffer = (UINT8 *)calloc(1, state->bytes);
For mode "1", state->bits == 1.
src/libImaging/TgaRleEncode.c then computes:
bytesPerPixel = (state->bits + 7) / 8;
This becomes 1, and the encoder uses pixel indexes as byte offsets:
static int
comparePixels(const UINT8 *buf, int x, int bytesPerPixel) {
buf += x * bytesPerPixel;
return memcmp(buf, buf + bytesPerPixel, bytesPerPixel) == 0;
}
The packet payload memcpy() later copies those out-of-bounds source bytes into
the output. Raw packets copy up to 128 contiguous bytes, while RLE packets copy
one representative byte:
memcpy(
dst, state->buffer + (state->x * bytesPerPixel - state->count), flushCount
);
A width
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Exploitation outlook
- Low exploitation risk0.31% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 24% of all EPSS-scored CVEs.
Advisory coverage (2)
External references
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